1. The Field of the Invention
The present invention relates generally to high speed data transmission systems. More particularly, embodiments of the invention relate to devices and methods for conductively connecting a flexible circuit to adjacent electrical devices such as, for example, a transmitter optical subassembly or receiver optical subassembly and a printed circuit board.
2. The Relevant Technology
Transceiver modules are widely used in the field of optoelectronics. Typically, a transceiver module comprises a transmitter optical subassembly (TOSA) and a receiver optical subassembly (ROSA). Each of the TOSA and the ROSA may have an optical receptacle, for example an LC cable receptacle or an SC cable receptacle, at one end for attachment to an optical cable and some device to enable a conductive connection to a printed circuit board at the other. The entire transceiver module, in turn, is connected to a computer system, such as a host system, for controlling the operation of the transceiver module. Thus, the computer system can direct the transceiver module to transmit an optical signal by directing an electronic signal through the printed circuit board and into the TOSA. The TOSA then generates an optical signal via an internal laser or light emitting diode (LED) and directs the optical signal into the outgoing optical cable. Similarly, the ROSA receives an optical signal via a photodiode from the incoming optical cable and transmits the signal to a printed circuit board and on to the computer system.
Providing an optimal connection between a TOSA and/or a ROSA and a printed circuit board, however, can be difficult. For example, within a transceiver module the TOSA and the ROSA must be positioned within small tolerances to achieve the desired optical performance. Similarly, the printed circuit board must typically be precisely positioned for its connections to adjacent devices. Adding a third layer of rigid alignment requirements (the PCB to the TOSA and/or ROSA) makes accurately positioning the devices difficult. Additionally, the TOSA and the ROSA often experience vibration and movement as optical cables are moved, attached and detached. The printed circuit board may thereby be damaged or even crack if it is rigidly attached to the TOSA and/or ROSA at one end and a transceiver module housing at the other. Differential thermal contraction/expansion can also cause problems if the devices are rigidly attached.
Accordingly, flexible circuits may be disposed between the TOSA and/or ROSA and the printed circuit board to electrically interconnect them while isolating the printed circuit board from vibration or thermal expansion or contraction of the adjacent devices. The flexible circuit is additionally advantageous in that, during production, the printed circuit board may be mechanically fixed in place while the TOSA and/or ROSA are not, or vice versa. Accordingly, a flexible circuit is frequently used for assembly of the module so that variations in device subassembly position do not prevent precise connections and alignments from being made between the TOSA and/or ROSA and the printed circuit board.
Additionally, the TOSA and/or ROSA may include a transistor-outline header to contain and protect the active devices within the TOSA and/or ROSA. The transistor-outline header (“TO-can”) in turn allows the electrical connection of the active devices in the TOSA and/or ROSA to the printed circuit board, via a flexible circuit board or otherwise. With respect to their construction, transistor headers often consist of a cylindrical metallic base with a number of conductive pins extending completely through, and generally perpendicular to, the base. One conventional method of conductively connecting a flexible circuit to a transistor header comprises pins on the transistor header that connect to reinforced openings on one end of the flexible circuit, which are then soldered to affix the flexible circuit and ensure reliable connections. In turn, the other end of the flexible circuit is attached to “finger” like traces on the rigid PCB, via soldering or otherwise. Such soldered contacts are typically aligned in a linear row along the edge of the PCB.
As optical devices such as TOSAs increase in performance and speed, however, additional conductive traces with different shapes and connectivity requirements are required. The number of such traces, as many as fifteen or more, often exceeds the capacity for conventional flexible circuit designs to make contact with adjacent electronic devices. Additionally, both because devices are manufactured according to industry standards and due to the industry pressure for increasingly smaller devices, simply enlarging the size of a contact interface is not always an option.
Accordingly, what is needed are novel devices and systems for improving the performance of conductive traces on a flexible circuit while simultaneously increasing the density of contacts at an interface with adjacent electrical devices.